This invention relates to a control apparatus for an internal combustion engine.
Recently, some types of internal combustion engines installed in automotive vehicles are equipped with a variable valve system which can variably control the lift amount, open/close timing, and other valve opening/closing action of intake valves and/or exhaust valves. The variable valve system variably controls these valve opening/closing action in accordance with a throttle opening degree and an engine speed or the like. More specifically, for example, the open/close lifting motion of the intake valve or the exhaust valve is selectively controlled by using a low-speed cam having a relatively small cam lift amount or a high-speed cam having a relatively large cam lift amount. To this end, a cam shaft is provided with the low-speed cam and the high-speed cam for controlling the valve opening/closing action. In this case, the engine operating region is separated beforehand into a working region of the low-speed cam and a working region of the high-speed cam. An appropriate cam is selected with reference to momentary values of the throttle opening degree and the engine speed.
Japanese Patent No. 2827768 discloses a variable valve system capable of selectively switching between a fuel economy-oriented valve operation mode and a power generation-oriented valve operation mode with reference to the engine operating region. The switching from the power generation-oriented valve operation mode to the fuel economy-oriented valve operation mode is executed at a specific throttle opening degree where no torque shock (i.e. no change in output torque) is caused in response to the switching operation. On the other hand, the switching from the fuel economy-oriented valve operation mode to the power generation-oriented valve operation mode is executed together with torque down correction including appropriate reduction of the throttle opening degree. With this control, it becomes possible to suppress or eliminate the torque shock occurring in the switching of valve operation mode.
However, according to the variable valve systems or various intake arrangements, the individual differences and aging changes of respective engines cause large difference and change in the charging efficiency. The engine control technique disclosed in the above-described prior art document gives no consideration on the individual differences and aging changes of respective engines. Therefore, due to the influence of such individual differences and aging changes, this conventional engine control technique is subjected to unpredicted control errors and accordingly cannot obtain desirable effects. Namely, unpredicted torque shock and air-fuel ratio fluctuation will occur. Accordingly, the drivability and the exhaust emission will be worsened.